1. Field of the Invention
The invention relates to shotshells. More particularly, the invention relates to shotshell basewad constructions.
2. Description of Related Art
A typical shotshell 20 (FIG. 1) has a hull which is generally analogous to the case of a small arms ammunition round. An example of such a shotshell 20 is the WINCHESTER XPERT shotshell by Olin Corporation, East Alton, Ill. The hull includes a tube 24, a basewad 26, and a metal head 28. The tube and basewad are usually separately formed but, not infrequently, may be unitarily formed. The tube is typically formed of plastic and may be of a type known the Reifenhauser tube. At the aft end 30 of the shotshell, the basewad is inserted in a tight fitting relation into the aft end of the tube. The cup-shaped metal head 28 surrounds an aft portion of the tube and is crimped to the outwardly-flared aft end of the tube and basewad to mechanically secure the three together and forms an annular rim 32 which is useful to assist in extraction of the hull from a shotgun (not shown) once fired. A central aperture 34 in the metal head 28 and co-aligned pocket 36 in the basewad accommodate a battery cup-type primer 38 in press fit relation. A propellant charge 40 is located in a powder chamber within the hull at least partially defined by a forward surface 42 of the basewad. An aft surface 43 of an over-powder wad illustrated as an over-powder cup 44 typically bounds most of the remainder of the powder chamber. The aft rim 45 of the over-powder cup may be close to contacting a forward rim 46 of the basewad. Thus, between the aft rim 45 and the forward rim 46, the powder chamber may be bounded by a cylindrical segment of the interior surface 47 of the tube 24.
A number of problems have plagued existing shotshells. Among these problems are the inadequate sealing of combustion gases against infiltration between the basewad and tube and against infiltration between the basewad and primer. A number of solutions have been proposed for such sealing problems. U.S. Pat. No. 3,359,906, of George L. Herter, shows a basewad with longitudinal arrays of angled annular sealing rings or teeth both on the outboard surface of the basewad and on the primer pocket surface of the basewad. Such teeth are respectively asserted as providing enhanced sealing against infiltration between the basewad and tube and between the basewad and primer.
U.S. Pat. No. 4,867,066 of Morris C. Buenemann, Jr., discloses the use of a ruptured disk-shaped injection molding gate on an interior primer hub surface. The gate provides an annular gas seal between the primer and the basewad.
The adoption of a one-piece compression-formed replacement for the separate basewad and tube eliminates the issue of infiltration between the basewad and tube. An early such one-piece configuration is shown in U.S. Pat. No. 3,351,014 of John S. Metcalf et al. A more recent example of a one-piece configuration is the WINCHESTER DOUBLE A line of shotshells by Olin Corporation. The DOUBLE A shotshell may include a one-piece wad visually similar to the wad of the shotshell 20 which may have an over-powder cup slightly smaller in diameter and slightly more compliant to engage the tapering inside surface of the compression-formed hull. Additionally, during the heading process (fitting of the metal head to the compression-formed plastic element) as the head is pressed forward and flattened onto the plastic hull element, a corresponding rearward pressure on an annular fixture inserted into the hull produces a channel in the basewad surrounding the primer pocket. Deformation of the plastic hull element via the impression of the channel provides for enhanced sealing with the primer.
Some users may still prefer hulls having separate basewads and tubes. Accordingly, there remains a need for improved two-piece combinations of a tube and basewad.